Gasoline is more powerful per unit weight than TNT. It is, therefore, not surprising that the internal combustion engine, even though operating at low efficiency, is able to power automobiles quite satisfactorily. Gasoline as a fuel contains nearly 500 times as much energy per pound as the lead acid battery.
It is estimated that the power source for an electric car should be able to store at least 100 watt-hours per pound of battery.
It appears that the use of metals in metal energy cells can provide a range in excess of 200 miles before refueling. Refueling consists of adding metal, water or reactant, and recovery of the reaction products for recycling and reuse, or disposal. The metal fuels that may be of use are Lead, Iron, Zinc, Aluminum, etc Of the alkaline metals, Lithium is particularly energetic and has certain advantage and disadvantages. However, the Aluminum-Air cell can take advantage of the existing, in-place and very large American Aluminum industry, which makes it a preferrable combination.
One finds in various publications a number of excellent descriptions of the theory and some test data for basic aluminum-air batteries. These are discussed in U.C.R.L. 8443, preprint by John Cooper et al, June, 1980; also, preliminary energy use and economic analysis of the aluminum-air battery for Automotive Propulsion, Interplan Corporation, Santa Barbara, Calif., report no. R7908, April 1980.
Aluminum and other metals provide a very energetic, recylcable fuel for powering general purpose vehicles. The energy storage, for example, per KG of aluminum is greater that 300 W-HR. and the specific power may reach 220 W-HR/GK. Howerver, there has been a need for the development of an engineered design of the critical components of the system which can be said to be workable and practical. Attention must be paid to the problems of fuel delivery, current collection and the achieving of ruggedness in delicate or marginal components.
It is anticipated that our invention will be useful in its concentration on a practical reactant cell which will provide the basis for a conpact engine and have the desired characteristics of ruggedness, as well as to provide for convenient replacement and maintenance of critical components.
The use of air cathode electrodes is well known in the art and they have been used sucessfully in a number of working cells. However, there has not been an appropriate negative electrode which can deliver high current, be conveniently replaced, and be free of corrosion effects. There has recently been valuable progress in lessening the corrosion by circulating and/or adding appropriate chemicals to the electrolytes. For example, Cooper, U.S. Pat. No. 4,154,903, issued May 15, 1979 describes a mechanically recharged calcium/air fuel cell with an aqueous NaOH/NaCl electrolyte. It is claimed that the use of the chloride provides a stable active electrode state. Struthers, U.S. Pat. No. 4,275,125 issued June 23, 1981, teaches the use of controlling the ph of the electrolyte by means of a novel addition of electrolyte. Other methods occur to those skilled in the art. Aluminum recently has been effectively and practically used to establish the anodes of air cells. Several of these methods have been published in the literature noted above.
U.S. Pat. No. 3,887,400 shows the circulation of slurry through battery cells to obtain higher current densities and good utilization of fuel. As mentioned in U.S. Pat. No. 4,147,839, excessive, slurry velocities have seemed to be needed to achieve uniformity of the slurry.
U.S. Pat. Nos. 3,414,437 and 4,147,839 also teach the use of active metal powders suspended in electrolytes. The slurries being contacted by metal stirrers to carry current from the cells high internal impedance appears to be inherent in such design.
In U.S. Pat. No. 3,592,698 the active powdered elements are carried on a conveyor belt moving across the face of a collector. Again, there have been devices used to form a slurry electrode by introducing eletrolyte to the cell bottom discharging is at the top. See U.S. Pat. No. 3,879,225. Other improvements are shown and discussed in U.S. Pat. No. 4,147,839.
In this invention the negative electrode of each of the desired number of cells is built up by deposition of active consumeable metal from a metal-electroyte slurry, by the action of induced gravitational forces. These forces are directed radially outward toward an anode current collector. The slurry is prepared outside our reaction chamber by methods known in the art; see, for example, "Selecting Agitator Systems to Suspend Solids in Liquids", Chemical Engineering May 24, 1976 by Gates et al.
Since the fuel is fed continuously at a rate determined by the energy requirements, we do not have to store quantities of metal in pockets, or in vessels. In our cells the reacting volume as illustrated in the drawings is repesentative of, but not restricted to a cell of cylindrical structure. Conical, in some cases has also been sucessful.
The cathode is preferably of gas or water type and several commercial units are available.
In our invention the metal is prepared in proper size, of chips, powder, etc. in a centrally located container from which the metal is "manifolded" to each separate reaction cell. Because the induced gravity forces cause deposition of the particles from the liquid, thus concentrating and compacting them, it is not necessary to use an extremely dense or rapidly moving slurry. Methods are used, but not shown here in detail, to vary electrolyte-metal concentration, to distribute the slurry to the reacting cells, and to control heat generation, velocities, heat dissipation, etc., and to control active metal to cathode or metal to hydrophilic separator distance etc. Various methods of eliminating electrolyte short circuiting are described elsewhere, for example, in U.S. Pat. Nos. 3,522,098, 3,537,904, 4,025,697, etc.
It is worthy of mention that U.S. Pat. No. 4,126,733 notes the possibility of reduced cell performance caused by the use of separators between the anode and cathode. In addition it is mentioned that without such separators, or the use of that patent's technique, shorting of the cells can occur if particles of active metal impinge on the cathode layer. In our invention we enjoy the benefit of a strong radially acting gravitational field which keeps active particles away from the cathode. Thus, although we may choose to have a very thin (or arbitrary) hydrophylic membrane, we are not bound to use such membranes.